The Magnifier

When jewelers work on small objects like the innards of a watch, they use what they call a magnifier which can be a lens mounted at one end of a tube as shown in Figure (1). The length of the tube is equal to the focal length of the lens, so that if you put the other end of the tube up against an object, the lens acts as an eyepiece and light from the object emerges from the lens as parallel rays. By placing your eye close to the lens, you get a close up, comfortably seen view of the object. You may have seen jewelers wear magnifiers like that shown in Figure (2).

Figure 1: A magnifier.

Figure 2: Jeweler Paul Gross with magnifier lenses mounted in visor.